This invention relates to blow molding machines and, more particularly, to an improved in-mold label dispenser for use with such machines.
Conventional blow molding machines include an extruder for extruding a parison of hot plastic between open sections of a mold. The extruded parison is clamped between the mold sections when the mold is closed and is then inflated by blowing air into the parison so that the parison assumes the shape of the mold. After cooling, the mold sections are opened and the molded part is then ejected from the mold.
Containers for various products are conventionally made by using blow molding machines. The containers are provided with labels, such as paper or paper/thermoplastic composite labels, in order to identify the products. The labels may be applied by gluing them to the containers after they have been ejected from the mold. The problem with these labels is that they often wrinkle or are improperly aligned on the containers. Moreover, they require a separate labeling step after molding which increases the cost of manufacturing the containers.
In more recent years, label dispensers have been developed which insert the labels within the mold prior to extrusion of the hot plastic parison and before closing the mold. Once the mold is closed with the label in place, the blowing operation that follows forms the hot plastic parison around the label to the shape of the mold and activates a heat sensitive adhesive which provides a permanent bond between the label and the container. These in-mold label dispensers thus effectively eliminate the need for a separate labeling step after the molded containers have been ejected from the mold. Moreover, labels applied by in-mold labeling add strength to the walls of the containers and thus allow the containers to be made with less plastic during the blow molding operation.
An in-mold labeling dispenser for a blow molding machine which has enjoyed considerable success in recent years is disclosed in U.S. Pat. No. 4,639,207 issued to W. A. Slat et al. on Jan. 27, 1987. This in-mold label dispenser is designed for use with a blow molding machine including a plurality of molds preferably arranged on a rotating wheel, each of the molds including mold sections that are movable between open and closed positions and which cooperatively define a mold cavity when the mold sections are brought to the closed position.
The label dispenser includes a label magazine for storing a plurality of labels to be dispensed into the mold and a dispensing head which is mounted for rectilinear movement along a first axis from adjacent the label magazine to between the mold sections in the open position of the mold. A label carrier is mounted on the dispensing head for rectilinear movement between retracted and extended positions along a second axis that is traverse to the first axis preferably in a perpendicular relationship. A drive mechanism moves the dispensing head and the label carrier in a coordinated fashion to transfer labels from the magazine to the mold for in-mold labeling prior to the blow molding operation. The label carrier includes vacuum cups for selectively removing one label at a time from the magazine and for holding the label in place as it is being carried to the mold.
During operation of the label dispenser, the label carrier is moved by the drive mechanism from the retracted position to the extended position with the dispensing head adjacent the label magazine whereupon the label carrier withdraws one label from the magazine. The label carrier is then moved together with the label to the retracted position while the dispensing head is moved to a position between the mold sections in the open position. The drive mechanism then moves the label carrier to the extended position where the label is deposited onto one of the mold sections within its mold cavity. The label carrier is moved back to the retracted position and the dispensing head is moved by the drive mechanism from between the mold sections to adjacent to the label magazine where the cycle begins again to deposit another label in the next mold.
Although these prior art in-mold label dispensers are designed to accurately place a label within a mold section of each open mold during operation of the blow molding machine, the location of the molds may vary as they rotate around the wheel to a position adjacent to the labeling station. As a result, the labels may be seriously misaligned when applied to the molded containers.
It is therefore an important object of this invention to provide an improved in-mold label dispenser for a blow molding machine which avoids the problems and difficulties of the prior art.
Another more specific object of this invention is to provide such an improved in-mold label dispenser which can accurately position the label carrier within each mold cavity for transferring a label thereto despite any variance in the location of the mold during operation of the blow molding machine.